U.S. Frost Dates by Weather Station

NOAA station USC00138806 · Iowa

Frost Dates for Webster City, IA

NOAA weather station Webster City (USC00138806), Iowa · elevation 1072 ft (327 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 16only 1 spring in 10 still has a frost later
  • Typical last frostMay 350% chance of a frost after it
  • Typical first fall frostOctober 250% chance of a frost before it
  • Frost-free season150 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Webster City, IASpring: a frost after April 20 in 9 years out of 10, after May 3 in half of the years, after May 16 in 1 year out of 10. Fall: the first frost comes before September 18 in 1 year out of 10, before October 2 in half of the years, before October 16 in 9 years out of 10. Typical frost-free season: 150 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 3First frost ~Oct 2Frost season at Webster City, IASpring: a frost after April 20 in 9 years out of 10, after May 3 in half of the years, after May 16 in 1 year out of 10. Fall: the first frost comes before September 18 in 1 year out of 10, before October 2 in half of the years, before October 16 in 9 years out of 10. Typical frost-free season: 150 days.JFMAMJJASONDLast frost ~May 3First frost ~Oct 2
frost likely chance fading 90% → 10% frost-free in a typical yearThe year at a glance. Blue: frost is likely; the gradient fades as the chance drops from 90% to 10%; green: the frost-free part of a typical year.

Frost dates (32°F)

Probability of frost, based on 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 16September 18
50% (typical)May 3October 2
90% (likely)April 20October 16
Frost-free season (32°F, 50% chance)
150 days
Hard frost (28°F), last in spring, 50% chance after
April 24
Hard frost (28°F), first in fall, 50% chance before
October 12

The last 15 years (2006–2020 normals)

Typical last frost May 2 (1 day earlier than the 30-year normal), typical first fall frost October 7 (5 days later). Frost-free season 156 days.

A shorter, more recent NOAA period. The 30-year normals above remain the main reference: 15 years carry more year-to-year noise.

Add these dates to your calendar Yearly reminders for the typical last frost, the lower-risk planting date and the typical first fall frost (.ics).

How the chance of frost changes with the date

Spring at Webster City: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 16, 20% May 11, 30% May 8, 40% May 6, 50% May 3, 60% May 1, 70% April 29, 80% April 25, 90% April 20. Observed last spring frost in recent years: 2021 May 12, 2022 May 4, 2023 May 4, 2024 April 25, 2025 April 17, 2026 May 12.Spring: last frostChance of a frost after this date10%50%90%May 1May 16May 3Apr 202021: May 122022: May 42023: May 42024: April 252025: April 172026: May 12Fall at Webster City: chance of a frost before this dateFall, chance of a frost before the date: 10% September 18, 20% September 23, 30% September 27, 40% September 30, 50% October 2, 60% October 4, 70% October 7, 80% October 11, 90% October 16. Observed first fall frost in recent years: 2021 October 17, 2022 September 28, 2023 October 10, 2024 October 7, 2025 October 22.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 18Oct 2Oct 162021: October 172022: September 282023: October 102024: October 72025: October 22
Two charts, because spring and fall answer different questions: in spring, the chance that a frost still comes after a date; in fall, the chance that the first frost has already come before it. NOAA publishes these odds from 10% to 90%, so the lines stop there. ◆ marks the actual date in each recent year.

What actually happened in recent years

Observed dates of the last spring and first fall frost (32°F) at this station; ◆ marks them on the charts above
YearLast spring frostFirst fall frost
2021May 12October 17
2022May 4September 28
2023May 4October 10
2024April 25October 7
2025April 17October 22
2026May 12season not over yet

What these dates mean

Setting out tender crops on the early spring date of April 20 brings a 90% chance of a light frost, making it a gamble for gardeners in Webster City.

The cautious spring date is May 16, when only a 10% chance of a light frost remains, while the cautious fall date is September 18, also with a 10% chance; counting on tender crops as late as October 16 carries a 90% chance of a light frost.

The 50% light-frost dates are May 3 and October 2; these mark the median odds for a frost occurring later in spring or earlier in fall. The 50% hard-frost dates are April 24 and October 12, and hard frosts at 28 °F can damage plants more severely than light frosts at 32 °F.

How to read the probabilities

The dates are probabilities from 30 years of weather, not a forecast for this year.

  • Spring: "10% after May 16" means that in about one spring out of ten a frost still happens after that date. The 90% date is the earliest: a frost after it happens in most years.
  • Fall: "10% before September 18" means that in about one fall out of ten the first frost arrives before that date.
  • 50% is the typical date: half of the years are earlier, half are later.
  • A light frost (32°F) damages tender plants; a hard frost (28°F) also stops most hardy vegetables.

Nearby weather stations

Map of weather stations near Webster City, IANumbered nearest stations: 1 — Fort Dodge, IA — 22 mi; 2 — Iowa Falls, IA — 28 mi; 3 — Boone, IA — 30 mi; 4 — Ames, IA — 31 mi; 5 — Hampton, IA — 36 mi.25 mi · 40 km1. Fort Dodge, IA — 22 mi12. Iowa Falls, IA — 28 mi23. Boone, IA — 30 mi34. Ames, IA — 31 mi45. Hampton, IA — 36 mi5
  1. Fort Dodge, IA 22 mi (35 km)
  2. Iowa Falls, IA 28 mi (45 km)
  3. Boone, IA 30 mi (48 km)
  4. Ames, IA 31 mi (50 km)
  5. Hampton, IA 36 mi (58 km)

Sources

* Hardiness zone 5a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 42.4686, -93.7975.